title: The minimal proteome in the reduced mitochondrion of the parasitic protist Giardia intestinalis.
abstract: The mitosomes of Giardia intestinalis are thought to be mitochondria highly-reduced in response to the oxygen-poor niche. We performed a quantitative proteomic assessment of Giardia mitosomes to increase understanding of the function and evolutionary origin of these enigmatic organelles. Mitosome-enriched fractions were obtained from cell homogenate using Optiprep gradient centrifugation. To distinguish mitosomal proteins from contamination, we used a quantitative shot-gun strategy based on isobaric tagging of peptides with iTRAQ and tandem mass spectrometry. Altogether, 638 proteins were identified in mitosome-enriched fractions. Of these, 139 proteins had iTRAQ ratio similar to that of the six known mitosomal markers. Proteins were selected for expression in Giardia to verify their cellular localizations and the mitosomal localization of 20 proteins was confirmed. These proteins include nine components of the FeS cluster assembly machinery, a novel diflavo-protein with NADPH reductase activity, a novel VAMP-associated protein, and a key component of the outer membrane protein translocase. None of the novel mitosomal proteins was predicted by previous genome analyses. The small proteome of the Giardia mitosome reflects the reduction in mitochondrial metabolism, which is limited to the FeS cluster assembly pathway, and a simplicity in the protein import pathway required for organelle biogenesis.
authors.affiliation: Department of Parasitology, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
authors.forename: Petr L
authors.initials: PL
authors.lastname: Jedelský
authors.forename: Pavel
authors.initials: P
authors.lastname: Doležal
authors.forename: Petr
authors.initials: P
authors.lastname: Rada
authors.forename: Jan
authors.initials: J
authors.lastname: Pyrih
authors.forename: Ondřej
authors.initials: O
authors.lastname: Smíd
authors.forename: Ivan
authors.initials: I
authors.lastname: Hrdý
authors.forename: Miroslava
authors.initials: M
authors.lastname: Sedinová
authors.forename: Michaela
authors.initials: M
authors.lastname: Marcinčiková
authors.forename: Lubomír
authors.initials: L
authors.lastname: Voleman
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Perry
authors.forename: Neritza Campo
authors.initials: NC
authors.lastname: Beltrán
authors.forename: Trevor
authors.initials: T
authors.lastname: Lithgow
authors.forename: Jan
authors.initials: J
authors.lastname: Tachezy
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016000:Cluster Analysis; D019143:Evolution, Molecular; D016829:Giardia lamblia / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D053142:Mitochondrial Size / Q000502:physiology*; D008969:Molecular Sequence Data; D010271:Parasites / Q000378:metabolism; D017510:Protein Folding; D055503:Protein Multimerization; D020543:Proteome / Q000032:analysis* / Q000378:metabolism; D053719:Tandem Mass Spectrometry
chemical_list: D024101:Mitochondrial Proteins; D020543:Proteome